An anesthesia system with a breathing gas source, an anesthetic evaporator and a breathing system with circulation of the breathing air has become known from DE 41 11 138 A1. The breathing gas reaches the breathing system from a compressed gas source via a dispensing valve, a flow meter and the anesthetic evaporator and is fed to the patient by means of a breathing gas pump. The anesthetic evaporator operates according to the bypass principle, which is based on branching off a partial gas flow from the gas flow at the input of the anesthetic evaporator, enriching this partial gas flow in an evaporator chamber for liquid anesthetic with saturated anesthetic vapor and then adding it back to the gas flow at the output of the anesthetic evaporator. The portion of anesthetic vapor in the gas flow can be changed manually by means of an adjustment part on the anesthetic evaporator.
The prior-art anesthesia system is designed for mainly manual operation.
An anesthetic dispensing system, in which breathing gas is conveyed by means of a switching valve in fast switching sequence either through an evaporator chamber provided with saturated anesthetic vapor or via a bypass line past the evaporator chamber, has become known from EP 146 220 B2 (U.S. Pat. No. 4,657,710). The concentration of the anesthetic in the breathing gas can be changed by means of predetermining suitable control signals for the switching valve in relation to pulse width and to frequency. Sensors that detect the corresponding physical parameters are necessary for the correction of deviations in concentration that occur due to changes in temperature and pressure, so that correction factors for the concentration delivery can be calculated in a calculating and control unit.
A large number of sensors and an electric power supply are necessary for the operation of the prior-art anesthetic dispensing system.